1. Field of the Invention
The present invention relates to a waveguide antenna apparatus and a polarizer, and relates more particularly to a polarizer having a stepped septum and a waveguide antenna apparatus using the same.
2. Description of the Related Art
In a microwave antenna system, a polarizer is utilized to convert a linearly polarized magnetic field to a circularly polarized magnetic field, or vice versa. Generally, different types of polarizer can be used in a microwave antenna system, in which a septum polarizer is one of the most popular.
A septum polarizer includes a waveguide. The waveguide may have an internal channel, which may have a cross section with a circular shape or a square shape. The metal septum is inserted into the channel in a direction along the longitudinal axis of the waveguide, dividing the channel into two equal sub-channels. An electromagnetic wave may be decomposed, by the septum, into two equal orthogonal projections, respectively parallel and perpendicular to the septum. Usually, the size of the septum is determined by a central operating frequency or wavelength.
However, traditional polarizers have several drawbacks. First, the bandwidth of the operating frequency of traditional polarizers is narrow, not satisfying the requirements of industrial applicability. Second, the square cross section of a traditional polarizer may easily exhibit cavity resonance phenomenon, and such resonance phenomenon may occur near the in-band frequency, negatively affecting signal quality. Third, when the operating frequency is greater than the X-band frequency (10 GHz), traditional polarizers cannot ensure the proper signal isolation between ports.
Thus, traditional polarizers still have many drawbacks, and development of a new polarizer is needed.